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How accurate is inertial positioning?
How is accuracy achieved in Inertial Positioning?  Is it possible to get 10 or 11 digits of accuracy without transmission of real-time corrections from a base (known) station? Is post-processing simultaneous data of Ref. & Rover required for getting the precise (10 & 11 digit) coordinates?

Hello K ARIVOLI, welcome to Aviation.SE. Can you please explain what you mean by 11&10 character coordinates? What units? GPS accuracy is normally expressed as a 95% bound on the horizontal, vertical or total distance error in the GPS position measurement.

Can you also clarify what "inertial GPS" is? GPS by itself isn't an inertial system, so it would be helpful if you can explain precisely what kind of system you're referring to.

"Inertial GPS"
Inertial navigation is separate from GPS navigation. Inertial navigation senses accelleration and uses that to estimate changes in velocity and hence estimate changes in position. GPS is a GNSS system that determines position from timing of satellite signals. There's no such thing as Inertial GPS although there are systems marketed as sat-nav which can use inertial navigation when GPS is unavailable (e.g. when driving through a tunnel).
10th Character
Digits are about precision not accuracy. Any sat-nav or GNSS receiver can produce location digits to much greater precision than their accuracy.
The number of digits, and their implications regarding accuracy and precision, depends on the units being presented. For example, I have a handheld GNSS receiver that I set to display UK Grid-references for convenience in conjunction with Ordnance Survey maps. The meaning of the 10th and 11th characters in terms of positional precision is therefore different.
TQ
395012
775012

In this case, the 10th digit is something like kilometers north of the OS origin. Accuracy of ±1 Km can certainly be achieved by unaugmented GNSS.
It is probably better to state a desired accuracy in terms of distance on the ground - for example many handheld GNSS receivers will display something like "Accuracy: 23 feet".
Base stations
All GNSS receivers (including GPS, GLONASS, Galileo etc) use multiple satellites to determine their position. Typically three or four are required for a fix. Pure GNSS receivers don't use base stations.
SBAS capable receivers (such as those that can use WAAS, EGNOS, etc) use additional satellites to achieve higher accuracy. They do not directly use base stations on the ground. The additional satellites transmit positional corrections that have been gathered from ground stations but the GNSS receivers do not receive data directly from the ground stations.
Higher accuracy GNSS units are used by, for example, site surveyors. These are larger and more expensive and in some cases do use ground base stations for greater accuracy.
Aviation
Generally, I don't think aviators have any use for knowing their aircraft location to centimeter accuracy in flight.
A GNSS with SBAS (e.g. GPS + WAAS) can provide the accuracy needed for  precision flight approaches but Garmin state "Currently, GPS alone does not meet the FAA's navigation requirements for accuracy, integrity and availability"
Glossary

GNSS = Global Navigation Satellite System.

GPS = Global Positioning System, US operated GNSS.
Galileo = EU operated GNSS.
GLONASS = Global Navigation Satellite System, Russian operated GNSS.
BDS = BeiDou Navigation Satellite System, China operated GNSS.

SBAS = Satellite Based Augmentation Systems.

WAAS = Wide Area Augmentation System = US operated SBAS.
EGNOS = European Geostationary Navigation Overlay Service, EU SBAS.

GBAS = Ground Based Augmentation Systems.

A good integrated system can do, and does, a lot more than just use inertial navigation when GPS is not available.

INS must, by it's principle, internally calculate latitude and longitude to at least 11 significant digits each to maintain reasonable precision. Nothing to do with UK Grid; everything happens in WGS84 only.

Rather than talking to (a single) base station, most aviation units will use signals from additional satellites to apply corrections.  In North America, the system is WAAS.
For a standard (civilian, single-frequency) GPS unit, the largest contributor to the positional error is the ionosphere model used. (See GPS Error Analysis page).     WAAS transmits data that allows the unit to apply a real-time correction to that model for locations over North America.  (Similar systems exist to do the same in other regions of the world).
From Wikipedia:

Actual performance measurements of the system at specific locations have shown it typically provides better than 1.0 metre (3 ft 3 in) laterally and 1.5 metres (4 ft 11 in) vertically throughout most of the contiguous United States and large parts of Canada and Alaska.


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What could be the reason for a feeling of speed oscillation after takeoff in a 747?
Took off from LHR in a B747-400 on Sunday and I experienced something new that is puzzling me.
After take off as the aircraft was climbing it seemed to continually speed up and slow down at the rate of once every one or two seconds. Kind of like an oscillation in the direction of travel.
After a few minutes of this it stopped.
What caused this to happen?

What was it that caused you believe it was speeding up and then slowing: a feeling of acceleration then deceleration physically, change of pitch of the airplane, change in engine noise, or something else?

Could have been gusting head/tailwinds - would cause both feeling of acceleration and pitch to change.

One "normal" reason for (a wrong) sense of airspeed oscillation could be the air conditioning pressure variation caused by a malfunctioning engine bleed or pack valve.

There are a whole bunch of possible reasons.
The first thing to note is that, from inside the cabin it can be very difficult to tell the difference between speeding up/slowing down, pitching up/down, and the rise and fall from turbulence (particularly when in a climb). And one I wasn't aware of but as pointed out by Sami, the air conditioning pressure varying because of a malfunction in the engine bleed or pack valve.
So why could it be happening?

Turbulence causing the aircraft to gentle rise/fall, which, in a climb, is fairly akin to small acceleration/decelerations - both to our inner ear, and in terms of what's physically happening to the aircraft
The air conditioning pressure rising and falling more than usual rather than maintaining a constant pressure
Slight pitch up/down manoeuvres, possibly from a relatively inexperienced pilot flying the aircraft
The auto-throttle throwing a hissy fit or, if climbing at 250 knots under 10,000 ft, oscillating slightly in order to stay at/below the 250 knot speed limit
The pilots adjusting thrust manually, possibly for the same reason as above
A gusting head/tailwind. Particularly noticeable near the ground and when in a climb, and can cause a feeling of acceleration/deceleration.
A malfunction in one of the engines causing the power to vary slightly. It's possible this was only noticeable at takeoff/climb thrust levels, and disappeared when throttling back

Typically you'd expect it to be due to either turbulence or a gusting wind, but there are several systems which could develop a small, fairly benign fault and have this symptom.
Edit: As noted by user Jamiec, Storm Katie (a reasonably strong storm) was over the UK at the time, which would certainly back up turbulence/gusting winds being the most likely culprit

A more general #4 would be the auto-throttle or auto-pilot in speed mode (at any speed) often does this, which is why I usually avoid the speed mode and use something more stable.

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Why do some military jets have needle-like structures at the nose and others don't?
I have seen some military jets have a needle-like structure at the nose and some others do not have that. Lockheed SR-71 Blackbirds have that structure and Lockheed Martin F-22 Raptors do not, why so?

(Image Source: www.aviationexplorer.com)

(Image Source: www.wikipedia.com)

Both of them are super sonic

I added pictures for reference, do you mean the little tube that the SR71 has branching off the tip of the nose or are you interested in the entire tip? In the latter case, you will see that the F22 has that as well....

SR-71 is not a fighter

yes,i mean little tube at nose,i checked Wikipedia and did not find it for raptor f-22,https://en.wikipedia.org/wiki/File:Lockheed_Martin_F-22A_Raptor_JSOH.jpg

@SentryRaven not all F22 variants have it, though: https://upload.wikimedia.org/wikipedia/commons/4/46/Lockheed_Martin_F-22A_Raptor_JSOH.jpg https://upload.wikimedia.org/wikipedia/commons/2/25/Two_F-22A_Raptor_in_column_flight_-_%28Noise_reduced%29.jpg

what will be the logic behind these tubes

Ah, it was later removed for the production version, the pitot tubes on the F22 are on the nose section, intergrated into the airframe and protruding only a bit to remain stealth.

@fawaz still from wikipedia: https://upload.wikimedia.org/wikipedia/commons/c/c0/Two_F-22_Raptor_in_flying.jpg

The SR71 seems to have the pitot tube branching off that main tip. The F22 had a similar concept for testing, but it got moved to the nose section later.

what is the advantage of pitot tube branching from nose?

I've seen pictures of research/test aircraft with various pitot tube extensions (booms) at the front, these are often removed for later production versions. My guess has always been that the longer data booms are used in testing to calibrate the simpler more robust inlets that will be used in production. The longer ones will be more "accurate" as they're well ahead of the body shock wave, but I guess they might be more sensitive to icing, blockages, or maybe even overheating. I've dug around for these sort of search words but haven't been able to find any confirmation yet...

Related: http://aviation.stackexchange.com/questions/7457/why-are-the-pitot-tubes-on-supersonic-combat-aircraft-so-long

@Andy - That's mostly it; the longer tube places the pitot well out into "undisturbed" airflow in front of the aircraft, where it can gather unbiased airspeed/altitude/VV data in initial test flights. That data is then used to compensate for airflow disturbance effects at the final pitot position. The longer test probe is delicate, not very stealthy, and is often less accurate at high AoA, so the test probe is removed after the production pitot system is calibrated. The SR-71 kept the nose probe because any other placement had accuracy problems, and the high-AOA disadvantage was a non-issue.

To skewer enemy soldiers...  At least that's the best answer I could come up with when I was like 3 y/o!

What you see on the SR-71 is an Alpha-Beta probe, with a pitot tube branching off the side of it. The nose cone of the SR-71 (and its variants) were changeable depending on its loadout.
From the A12 Configuration:

The sharply tapered nose section was pressurized and contained navigational and communications equipment, a
  remote compass transmitter, periscope optics, air inlet computer and angle transducer, and other radio equipment.
  A combination pitot-static and alpha-beta probe was installed at the forward tip to capture airspeed and altitude data.

About the SR-71 versatility

The SR-71 also served as a testbed for an Optical Air Data System (OADS), a fiber optic device using laser
  technology to replace the pitot tube (airspeed probe) on high-performance aircraft. It used laser light instead of air
  pressure to produce airspeed and attitude reference data such as angle of attack and sideslip normally obtained with
  small tubes and vanes extending into the air stream or from tubes

Both sources above: Design and Development of the Blackbird
The F22 serves quite a different purpose to the variants of the Blackbird, and thus probably has less need for sensitive sensor equipment of the SR-71. It still has a pitot tube which can be seen in the photo you posted

And it, no doubt gets other avionic information from a traditional pitot-static system rather than rely on an alpha-beta probe as the Blackbird did.

As a "new generation" fighter with a complex control system I'd suggest that the F22 has just as much need for sensitive sensor equipment as the SR71. I'd say that the reason that the F22 has moved the pitot-static probes and AoA, AOS sensors to the fuselage is that sticking a nice big metal pole on the nose right in front of the radar on the F22 probably causes a few palpitations for the radar engineers and would not be considered "a good thing" to do.

Some explanation of what an alpha-beta probe is would be good. Wikipedia search hits radiation counters but I'm guessing that's not what these are?

@RussellBorogove Seconded. I’ve been around this site for a long time and, while I wouldn’t call myself an expert by any means, I know way more about aviation than the average member of the public. And I’ve never heard of an alpha-beta probe. Kevin, please at least add a link to explain what one is.

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How are aircraft identified as unregistered?
When someone operates an unregistered vehicle on public roads we know how they are caught: Police routinely pull people over, and they always check registration of vehicles.  In fact, police will frequently "run tags" without even stopping cars.  They have a realtime connection to a nationwide registry that can report the details of the tagged car and whether a tag is expired or stolen.
Apparently there are a good number of fines and prosecutions for operation of unregistered aircraft.  And at least some are reported by ATC.  I'm going to assume that nobody is foolish enough to file a flight plan listing an unregistered aircraft ID.
So how does ATC check aircraft registration?  Do they have live access to the registry?  When someone calls an ID over the radio are there controllers that routinely check the ID's registration?  Is it illegal to make up an ID for radio interaction with ATC?  Are there people that visually watch for tail numbers and discrepancies with radio calls?

Are you asking about a specific country? There's a big difference between the US, where private GA flying is essentially anonymous (like using your own car), and other countries that charge ATC fees. The countries that charge user fees may track and record tail numbers and interactions with ATC for billing; the US has no reason to do that.

@Pondlife - I did not know that!  Then yes, this question is about the U.S.

@feetwet: In general, unless you have a reason not to, assume a global audience. Because you do have a global audience. Seems you took the opposite approach here, for some reason assuming you were talking only to your countrymen.

@LightnessRacesinOrbit That's good advice, but questions about only one country are perfectly fine as long as that's stated/tagged correctly. Many regulatory and procedural questions can only have country-specific (or at least regulator-specific) answers, and we have a lot of those questions in aviation.

@Pondlife: It wasn't originally stated/tagged at all. I'm sure the OP shall now be sure to do so in the future.

Reading from the link posted by @mins in another question and noticing a pattern, reading between the lines. The first entry from 2008 was in FL and he had intalled extra fuel tanks. Florida, extra tanks, smuggling anyone? 2nd entry, also in Florida appears to involve some kind of fraud. The 3rd and 4th are the same case and was reported by ATC. It also originated in FL. I would say Florida ATC is probably more vigilant of private aircraft due to the amount of smuggling that goes on there. The one in Idaho says FAA is supporting an IRS investigation. The next one is an INS investigation.

The referenced question is about pilot who are not certified (no pilots license), not about planes that are not registered!

Aircraft don't have to be actually flying for people to notice something fishy going on. In particular, there are always people hanging about at airports keeping an eye on everything going on. Furthermore (at least in the US), aircraft registration details are a matter of public record and can be easily looked up online.
For example, here is the registration detail page for John Travolta's private Boeing 707: https://registry.faa.gov/AircraftInquiry/Search/NNumberResult?nNumberTxt=N707JT
As you can see it contains complete registration details including type, validity status, expiration dates, owner name and address, and airworthiness status.

So how does ATC check aircraft registration?
They don't, that isn't their job. The only time that anyone will ask to see your registration in normal circumstances is during a ramp check, and those are done by FAA inspectors. There are probably some other 'routine' checks, like a checkride examiner verifying it as part of the checkride or your insurance company asking for a copy. I suppose it's also possible that your state might want to see it for some tax-related reasons.
Do they have live access to the registry?
I have no idea, but as Greg pointed out the registry is open to anyone with an internet connection so it's at least possible that they do. But I don't really see how any of the registration information would be relevant or useful to ATC operations anyway. One possible exception could be search and rescue: I guess the registration information might be useful for contacting the aircraft owner if the aircraft is missing.
When someone calls an ID over the radio are there controllers that routinely check the ID's registration?
Again, I have no idea, but I can't think why ATC would want or need to check it and I couldn't find anything in the ATC orders about checking it.
Is it illegal to make up an ID for radio interaction with ATC?
I couldn't find any specific regulation about that, but if the FAA wants to enforce it then I'm sure they'll find something. They could always fall back on 91.13 and claim that by lying to ATC you're displaying reckless behavior. And if the government really wants to get serious with you then they could charge you under 18 USC 1001: lying to a federal government agent is a criminal offense.
Are there people that visually watch for tail numbers and discrepancies with radio calls?
Yes, they're called planespotters :-) I'm only half-joking: some people are obsessive about things like that, and it wouldn't surprise me at all if someone out there likes to look up the owners of aircraft he hears on the radio.

Except that browsing these reports at least several of the ones I've checked say something like, "air traffic controllers identified aircraft N5863S as an unregistered civil aircraft...."  So ATC does appear to check registration.  (Again, maybe only pursuant to some airspace rule violation, but the reports I've seen don't suggest that.)

Those seem more to be, post issue, and usually done by office staff people, not the operational day-to-day controllers

ADS-B and mode S transponders transmit your aircraft's ICAO number which is like the VIN number on your car. All the registration, owner, tail number, etc will be referenced to that ICAO number. I'm sure modern ATC systems, after interrogating the transponder can automatically pull up the aircraft type and tail number from a database. It's quite possible that it will flag unregistered aircraft on their screen.

On Flightradar 24 the data for ADS-B aircraft are collected by private ADS-B receivers. If you click on a plane it has the tail #, and if a flight plan is filed it has the origin & destination. So obviously even their system pulls this data from a public database. It would be very simple to have a computer flag any unregistered plane.

@TomMcW That might be possible for large commercial aircraft, but this question is about GA aircraft which, at least in the US, aren't required to have ADS-B or even a transponder. Even after ADS-B becomes mandatory in 2020, it's only required for some airspace and there'll still be large areas of the US where you don't need it. There's a lot of relevant information in this question.

@feetwet I'm sure ATC have identified illegal aircraft in some cases, but as far as I know and can tell from their documented procedures, it isn't something that's a basic task for them..

@Pondlife I was thinking about that. I looked, but couldn't find any info on how ATC systems get info on non-ADS-B aircraft if there's no flight plan filed. They prob enter their tail number in manually when they check in. I'd bet any aircraft that is seriously overdue on registration will have its tail # flagged. You were saying that ATC probably doesn't routinely check registrations. As busy as they are you're probably right, but the OP said that ATC had reported some of them, so their system probably does it for them. Of course one could be careful never to have to check in w/ ATC

@TomMcW That might make a good question :-)

"Is it illegal to make up an ID for radio interaction with ATC?" Wouldn't that fall under incorrectly identified and/or unlicensed radio transmission? Which would fall under the FCC rules in the US, and their counteparts in other parts of the world.

I wonder how strictly "deregistration" is enforced: could you just pick an ID of a scrapped plane and fly under "assumed identity" of something from a junkyard? It would be pretty hard to spot if you used only private, field landings.

Regarding the callsign: Pilots will occasionally call up using some made-up callsign that may or may not be based on their tail number (medevac helicopters are frequent offenders). Unless the controller is feeling especially combative, all that happens is we roll our eyes and sigh before responding. It is against the rules, unless they have a specific LOA so everyone knows about the special callsign, but it's not worth getting bent out of shape over it.


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How does a fire suppression system work?
On fire events, some aircraft have a complex system, usually called a Fire Suppression System.
Where are they located? Do they work automatically, or it is necessary for the crew to activate them?

The fire suppression system in an aircraft uses both passive and active systems to reduce and eliminate fires. Passive methods include the use of noncombustible materials, separation by routing, compartmentalization (use of firewalls), isolation, proper ventilation and drainage. The active methods include fire detection and extinguishing systems.
The fire extinguishing system in the aircraft consists of a number of components (excluding the fire detection system), which includes,

Portable (handheld) fire extinguishers in cockpit and cabin,
Fire extinguisher bottles for engines and APU
Cargo hold fire extinguisher systems and
Fire extinguishers for toilet waste bins.

All the transport aircraft are required to carry a minimum number of portable fire extinguishers depending on the number of passengers carried. The following table gives the minimum number of portable fire extinguishers to be carried in transport aircraft (the cockpit should have a minimum of one).

Table from FAA document Fire Protection Systems
In case of cabin (or cockpit) fire, the portable fire extinguishers (usually, $CO_{2}$ extinguishers are not used) are used by the crew to extinguish the fire.
The engines and APUs have their own fire extinguishing systems, which have a liquid halogenated extinguishing agent and pressurized gas stored in fixed (typically steel) fire extinguisher containers, which are discharged on pilot command.
The engines have their own fire extinguishing systems, which usually have a pair of fire extinguishing bottles (or a pair for each engine), which supply extinguishing agent (Halon 1301 or Hydrofluorocompounds) to the engine.

Image from Boeing Aero magazine- Fire Protection: Engines and Auxiliary Power Units
The fire detection system from each engine displays the status in the cockpit, which warns of any engine fire. In case the pilot pulls the fire handle, the fuel flow to the engine is shut off and an explosive cartridge is fired in the fire extinguishing bottle, releasing the agent into the engine.

Image from FAA document Fire Protection Systems
The APU fire suppression system is similar to the engine fire suppression system, though only a single fire extinguisher bottle is used. Again, the fire extinguisher operation is commanded by the cockpit crew and results in the shutting down of the APU and the source of air.

Image from Boeing Aero magazine- Fire Protection: Engines and Auxiliary Power Units
In ground, the APU fire extinguishing system can operate automatically.
The cargo hold fire extinguishing system is similar to the above, where the crew can activate the fire extinguishing system if the smoke detectors in the cargo hold activates the warning lights in cabin. The extinguishing system is of two types- a dump system that releases the extinguishing agent directly
when the cargo fire discharge switch is activated or a metered system, where metered bottles discharge slowly which keeps the correct concentration of extinguishing agent in the cargo compartment to keep the fire extinguished for 180 minutes.

Table from FAA document Fire Protection Systems
The toilet waste bin is the only place in the aircraft with an automatic fire extinguishing system (in addition to ashtrays), where the heat sensors (not smoke detectors) trigger fire extinguishers.

Some aircraft have On Board Inert Gas Generating System (OBIGGS), which is used to 'inert' the fuel tank using nitrogen (usually generated by membrane based gas separation).

In commercial airliners, there are usually two places where fire suppression systems are installed: the cargo compartment and the engines. Take the Boeing 777 for example, it has fire detection and extinguishing systems in the APU (which is technically an engine as well), cargo compartments, engines and lavatories; the crew rest compartments and main gear wheel wells come with fire detection but no extinguishing system.
Fire detection consists of two sensors. To prevent false alarms, both sensors must sense the presence of smoke for the alarm to be sound. The sensors has self fault-detection capability. One of the items on the pre-flight checklist is to activate the test circuits and see if the fire alarm sounds.
Fire suppression systems work by spraying a chemical agent.
When smoke is detected, an aural alarm is sound in the cockpit, along with red lights which indicate where is the fire. A message will also be shown in the flight computer screen (if the cockpit has one).

For most systems, the pilots have to manually pull the handles to activate fire suppression. Take the engine fire extinguishing system in a Boeing 777 for example, there are two engine fire extinguisher bottles. Either or both bottles can be discharged into either engine. It is up to the pilots to follow the emergency procedures, or make a judgment call if they think the pre-established procedure is not the best course of action in a given situation.
The lavatory fire extinguisher, on the other hand, is automatic.


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Can someone provide details about airlines dividing crew into personality groups?
In this answer about crew bidding/scheduling, it's mentioned that crews may be divided into groups based on personality.
What personality traits may be considered? How are people matched? Is this common around the industry?

Will have you an answer by tomorrow, there are 7 groups, the criteria will I look up. This is a ME3 carrier

I spoke to my friend at the one of the ME3 carriers. She tried to find any information regarding this matter but was not able to find it. However during your recruitment process you have to perform a personality test and based on this test you are placed in one of the total of 7 groups. During the scheduling they combine people from different groups so that there is a balanced and workable crew on board. Say that you're in group 5, then you will for example mostly work with people that are in group 1 and 3.
Questions on this personality test are like:

Would you rather (example: clean a room or work within a group)
Which statements best describes you? (leader, selfish, friendly, etc, etc)

These airlines are run on performance optimization and care less about human values.

They group crews with like personalities? Great, I just got on a plane where all the cabin staff answered selfish to the 2nd question. Guess I can forget about getting a bag of peanuts. :/

I suspect most large airlines use seniority for bidding and schedules. Certainly most North American airlines do.
When using seniority it is impossible to assign flights or monthly schedules based on personality. Many bidding systems can allow an individual to request to not fly with an individual crew member, but this is still constrained by seniority.
In rare cases management may intervene to separate individuals who have extreme personality conflicts.


text:
What methods are used to perform head tracking in the cockpit?
In this question, I asked about a helmet with built-in HUD, and have a follow-up question:
What methods are used (or have been used) to perform head-tracking in the cockpit?
The website for that particular helmet (which I'm surprised exists like it does ... could I simply order one? doubt it ...) has the following (edit: here is additional information for that helmet):

High-speed tracker with a full-spherical Field of Regard(FOR); choice of Hybrid-Inertial or Magnetic tracker

Almost certainly an accelerometer - any other techniques would likely cause severe interference with existing aircraft systems

Related: XinReality Head-mounted display

The only reasonable method is accelerometer or gyro sensor, but not only one, about 3 of them to make precise tracking without any bugs, as the plane would tilt too, it would be reasonable to have acclereometers to calculate that too to make the exclusion of any bugs and unwanted tilts

"about 3 of them to make precise tracking", 3 are required because we live in a 3D space and accelerometers / rate gyros are usually sensing only on 1D. Having only one would be like having only cones of one type in our eyes. We would see the world partially and in gray shades. Here a LSM330DLC, a chip with 3 accelerometers and 3 gyroscopes combined.

What i meant is 3 diferent chips, in diferent superficies of the helment to make absolutely precise tracking, one chip can always interfer with some noise or unwanted bugs, you can take by example a simple smartphone that has bug like once a 1 minute

That isn't the typical use of the word "bug". This, and other words/phrases, make your explanation difficult to interpret.


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Is is possible to use non-hydraulic fluids in a hydraulic system in an emergency?
In this answer, Ralph wrote:
Spare fluid is common enough to have on-board to replenish the resevoirs.

After reading that, I recalled an incident I was told about nearly twenty years ago about a hydraulic failure on an Aeroflot flight, where Lemonade (a Russian soft drink of sorts) was used in a pinch. I've always wondered about the authenticity of this story.
Is it true? Is it plausible? Have there been other times where some non-ideal fluid was used in place of hydraulic fluid?

Related: Russian Plane Comes In On A Wing And Lemonade

@mins Thanks for that! I didn't even think to do a search. I wonder if it was real or just a colorful addition to the story...

Apart from the Lemonade example, what do you mean by non-hydraulic fluid? Compressible fluid, or fluid other than standard hydraulic fluids such as 5606 or Skydrol?

Please note that the lemonade was used only for very short time and on very low altitude - from discovery that landing gear won't extend, they took only as much time to circle as it was necessary to pour the lemonade in, and then landed immediately. So most of the extreme conditions that regular fluid has to endure (freezing temp, low pressure) didn't apply here.

@JonathanWalters I mean anything ... I honestly don't know much about hydraulics.

Is it possible? Sure. Theoretically. Once.
I can't speak to your Aeroflot scenario without more details, but broadly speaking any liquid will work as "hydraulic fluid" within certain limits: At the most basic level all that is required is that it be incompressible and flow at an acceptable rate (i.e. It is a liquid with a viscosity that falls within a certain range).  Engine oil is frequently used as a hydraulic fluid for certain applications (constant-speed propellers on small aircraft), and special-purpose hydraulic oil for others (the brakes on small aircraft).

There are some challenges to using any old liquid as "hydraulic fluid" though, which are why I say this is only theoretically possible (and probably only once). The two big concerns are the fluid's operating temperature range - its freezing and boiling points - and its corrosion potential.
Let's consider MIL-PRF-5606H (a typical hydraulic oil) and ordinary lemonade as examples:
Operating Temperature Range
In terms of temperature 5606 hydraulic oil has a much wider operating range than lemonade: It's "pour point" is below -60°C and its boiling point over 175°C, while lemonade's operating temperature range is probably close to water: It will freeze somewhere close to 0°C and boil somewhere close to 100°C (the exact numbers will depend on the chemical composition of the lemonade).
If we use both of these fluids in a brake system there is a chance the lemonade will boil when the brakes are applied (creating a gas pocket that's compressible, and reducing brake effectiveness), or that it will freeze in flight and the brakes will fail to apply because the ice is blocking the lines.
Corrosion Potential
As far as corrosion potential 5606 hydraulic oil is a mineral oil with some red dye in it: Since it doesn't contain dissolved water or electrolytes it's generally non-corrosive. Lemonade on the other hand is nothing but water and dissolved electrolytes (mainly citric acid to make it taste like lemon) plus sugar and a few other things. If we ran hydraulic actuators on this stuff we should expect them to corrode (rust) and eventually fail.
So it's possible that under the right circumstances an airplane could complete a flight with lemonade, water, etc. as "hydraulic fluid", but having done so the maintenance department will have to purge the "creative" fluid from the system, and probably follow some steps to remove any corrosive residue from the system (possibly up to and including replacing major system components). Long term operation in such a condition would probably damage components to the point where many of the system's moving parts (actuators, valves, etc.) would need to be replaced.

In short, yes!
The thing is, a fluid is fluid. Any fluid that is similar to water or oil can be used. But, you would need to be on the ground and have enough of that fluid. Also, using such a fluid will introduce potential damage and corrosion to the system, so a flush should be done as soon as possible.
In addition, there might be hydraulic systems that experience higher temperatures, like brakes - in that case, regular water would be a bad idea or anything water based.
Lemonade is a a carbonated drink, and using carbonated drink as a hydraulic fluid is a bad as it would emit a lot of gas, and has significantly lower boiling point. So I would speculate that if they did use it, they probably let it vent out all the CO2 first.

Lemonade is not typically carbonated... at least not in the US.

Lemonade is a brand of Carbonated drink in Russia, so I assume that since it's Aeroflot, it's carbonated lemonade ;)

Some (many?) aircraft do have hydraulic fluid reservoirs for their hydraulically actuated landing gear systems that can be checked and replenished in the air.

In LR-JET type airplanes Learjet uses an emergency air bottle in the event hydraulic fluid is lost.  The emergency air is pressurized between 1800 and 3000.  When the bottle is opened to extend the gear or apply pressure to the brakes, the air will move shuttle valves causing air pressure to extend the gear or stop the airplane.
I know it is not the same as replenishing it with some soft drink but it does answer the question of whether or not something like this is possible.

I know a few military airplanes that have a similar system of emergency gear extension. But I guess it would be much harder to keep, say, control surfaces operational in this manner. (On the other hand, on non-FBW aircraft this may not be necessary).

1800 and 3000 what ? https://en.wikipedia.org/wiki/Pressure#Units

1800 o'clock and 3000 ft AGL ;)


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What techniques, tools, or instruments are used while performing zero-g parabolic dives?
There are companies that sell "zero g" rides, where the aircraft is configured specifically to take people and possibly experiments through a parabolic dive to experience a short period of micro-gravity (possibly not the proper term).
This question asks about possible risks associated with the maneuver.
I'm interested in what specific techniques, tools, or instruments are in the cockpit that allow the pilots to properly follow the proper trajectory, while not pounding the occupants against the walls of the aircraft?
A G meter seems pretty obvious, but are there other less common things used? Are there special techniques for managing energy buildup, or for reminding the pilot when to pull out of the dive so as not to over-stress the air-frame?
Any other interesting information that I may not be thinking of in a similar vein is also welcome.

Are you interested from a commercial aircraft perspective, or aerobatics in general?

Heh, your use of "reminding" is amusing. As if the pilot might "forget" that the aircraft is in freefall! :)

@RonBeyer More specifically, what might be in use on an aircraft used by this company or this company. Due to the specific mission of the aircraft, there might be specialized things in the cockpit.

Related: Airbus A310 Zero-G. Nothing is really explained, just "With a glass cockpit and a new flight control system...". On the other hand it doesn't seem so difficult.

@mins I would think that any slight deviations from the ideal flight path would lead to people getting smashed into a wall...

Also from that link is this statement: "At the top of each curve, the forces on the passengers and objects inside cancel each other out, causing everything to float in weightlessness." Which is technically not true, the weightlessness exists at other points than just at the top of the curve...

A related question mentions that there is a device on the yoke so one pilot controls only axis and the other only the horizontal

@TomMcW Hmmm... That almost answers this question I think.

I tagged my own question as a duplicate, as the answer in that question should be pretty definitive, as it came from someone at one of those companies. The question is different, but the answer applies.

I'm an aerobatic pilot, with exactly 0 hours of turbine time, so this is a guess:

Climb to altitude and establish a predetermined airspeed.
Gently push to an 'A' degree nose down attitude, and maintain throttles at 'B'(accelerate to the highest airspeed permitted)
When airspeed indicator shows 'C', gently pull up to a nose-up attitude of 'D' (use the G meter to ensure you do not exceed 'E' Gs)
When airspeed indicator indicates 'F', reference the G meter and slowly push over to 0 Gs.
Monitor the changing pitch attitude and airspeed.  Warn the passengers when certain limits are passed.  (i.e., 10 seconds to recovery)
When nose-down pitch of 'G' is achieved, stop pushing and begin pulling back to level flight, taking extreme care not to exceed Vne (or other appropriate limit) and the G limit of the airplane.

Instruments required: Altimeter, Airspeed Indicator, G-meter, Attitude Indicator

There is no single moment where the attitude would be fixed. You are either pushing 0 G, which is a parabolic trajectory, or pulling 2 G, which is also parabolic trajectory, just upside down.


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Which hand do fighter pilots use for the control stick?
Here is a question that has been bothering me for a while. Do right-handed fighter pilots use their right hand to hold the control stick? And do left-handed fighter pilots use their left hand?
Or is it the other way around? Or do they maybe use both hands a lot of the time? It also brings up the question as to what the other hand is expected to do and which side of the cockpit the most common control buttons are on.
My guess is that since most people are right handed, they use their right hand. There's also triggers on the yoke so it seems all the more likely that the right hand is used for right-handers.
I'm asking because you look at video games and their controllers. They always use the left joystick for moving the character. In the case of flight simulators, the left joystick is used as the 'stick' or yoke. So you're pretty much left with no choice but to use your left thumb. Not saying this is awkward for video games, however, on those big joysticks for PC games, I remember I always used my right hand.
Also, let's ignore civil commercial piloting because those seem to usually use steering wheel type controls, not a traditional stick. Please let me know if you're a fighter pilot when you answer, because the triggers on the yoke have an effect on which hand you're most comfortable with.

A large proportion of civil airliners are Airbus aircraft. These all use a side-stick controller. In the left seat the stick is held in the left hand. In the right seat, the stick is held in the right hand. Pilots have to be able to use either hand.

Thanks never knew that before. TBH i kinda marvel at that because it just seems so awkward to control a yoke not centered in front of you.

most aircrafts are designed for right-handed. Left-handed just adapt. I read somewhere (cannot find the source) that Airbus' studies before launching the A320 (first aircraft with sidestick on the left for the pilot on the left seat) showed that even the right-handed adapt well for using the left hand to pilot.

@user1705043 FYI, while it's true that fighter pilots typically fly right-handed, the opposite is true for most civilian aircraft. The pilot-in-command is usually sitting in the left seat with left hand on the yoke or sidestick and right hand on the throttle(s)/thrust levers or whatever other control. Of course, for aircraft with 2-person crews, the FO sits in the right seat and flies with his right hand. This may be the primary reason that a flight-sim game would default to left-handed controls.

even with "steering wheel" type controls you only use one hand to operate them with the other hand for the throttle/thrust levers.

Can't speak to fighter jets, but in light aircraft with joysticks - mostly gliders - I would use either hand.  With 'steering wheel' yokes, I'll mostly use my left hand even through I'm right-handed (and sitting in the left seat).

Most fighter pilots, regardless of their handedness, use their right hand to fly the stick, and their left hand to move the throttle(s)/PCL (Power Control Lever). This is just how most fighter cockpits are set up, with the power on the left side.

The sticks are also not really usable for a left hander because a few of the buttons would be inaccessible with a left hand on the stick. In some cases (like the F-16), the cockpit uses a sidestick layout, with the stick on the edge of the cockpit, rather than in between the pilot's legs.

So no, it would not really be possible for left-handed pilots to fly with their left hand on the stick for long periods of time (I will note, that if you need to select something on the right side, most will hold the stick lightly in their left hand for a brief second, actuate the item with their right hand, and then switch back) unless the entire cockpit were redesigned, which is just not worth it.

I had suspicions that the stick shape was assymetric such that only a right-handed grip was feasible, as the first photo shows, but never imagined a non-centered stick like the F-16. How does that work doing sharp maneuvers? Depending on whether the g-force is to the left or the right, that stick will be hard to push won't it? Wasn't the F-16 designed as a dogfighter? I'm just marvelling at how awkward that side stick seems to me.

Yes, the F-16 is quite capable of aerobatics but G-forces are much less lateral than longitudinal/vertical (i.e. percieved Gs are pushing you into your seat rather than side to side). Additionally, the F-16 is a "fly-by-wire" aircraft, meaning it is electronically controlled rather than mechanical linkage from the stick. Initially, the stick didn't even move, just sensed the force input by the pilot on the stick. But after that felt weird to pilots/caused strains, they allowed the stick to move, though it remains fly-by-wire

I guess that's a good point I never realized. After all, how often do you pull a sharp yaw at 3+ g's? I guess they always roll first and pull back on the stick, making the local g force point down into the seat.

@user1705043 To answer your question, hopefully never. Yawing that quickly without banking puts you in a spin (if it doesn't cause the plane to disintegrate first.) Additionally, it means you will have a bad day.

Airframes are designed to only be able to load high g-forces towards the belly of the aircraft.

I am an ex-military pilot and retired airline pilot who is still an active pilot in general aviation.  The simple answer is that single seat and tandem seat cockpits are set up with the throttle and trim on the left, so that the stick has to be handled with the right hand.
With a few exceptions side by side cockpits have wheels and the throttle and trim are between the seats so that the pilot in the left seat, usually the pilot in command, uses his left hand on the wheel and the other pilot uses his right hand on the wheel.
I never have trouble switching back and forth, but some people do.

Its not just fighter planes that have the stick in the right and power in the left. That's the way tandem (front-and-back seating) aircraft are set up in general. You can see the throttle on the left-hand wall in this Citabria:

And gliders and helicopters are also set up with "the stick" in the right hand and "power" in the left.
Even though a glider doesn't have an engine, most of them have some kind of airbrakes, which are deployed just as if it was a throttle. Pushing the lever forward with the left hand decreases drag and pulling backwards increases drag. This isn't the same as thrust, but to a power pilot, it feels fairly natural to push forward to go faster and pull backwards to go slower. The speed brake handle in this glider is the blue handle on the left.

In a helicopter, the right hand (no matter which side the pilot sits on) is for the cyclic, which (for the post part) controls pitch and roll, and the left hand controls the collective and throttle, which together work to add and remove power from the aircraft. This also feels fairly natural to pilots who are used to stick in the right, throttle in the left. The big difference is that the collective is an "up/down" control like a Johnson bar, not a "forward/back" control, and you put it down to reduce power and up to increase power. Furthermore, the throttle, when manually controlled, is a twist grip on the collective, which operates more like a motorcycle throttle.  You can see the heli controls in this simulator.


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How do GA glass cockpit attitude indicators handle aerobatics?
For example, consider you are flying the 8KCAB Super Decathlon (a fairly common acrobatic plane) that had G1000 (using the flagship Garmin glass cockpit as an example, answers for other types of GA glass are welcome) avionics fitted to it, and you were about to go off and practice your favorite aerobatic routine in the local aerobatics box.  Would you have to do anything equivalent to "caging" in order to keep the attitude indication functions of the G1000 from misbehaving during aerobatic maneuvers, or is that not an issue with the types of "glass cockpit" instrumentation used in the GA world?

I fly a Super Decathlon with an Aspen E1000.  While an excellent PFD, I certainly would not trust it in aerobatic flight.  There's no cage function, and no way that I'm aware of to keep the attitude indicator from misbehaving, which I've seen it do firsthand.
I also fly the Avidyne R9 system, which also does not have a caging function.
Furthermore, I downloaded the Garmin G1000 manual, which says nothing about a way to cage the GRS 77.
This lack of commonly available GA glass-cockpit aerobatic-capable instrumentation  probably contributes to why one does not do aerobatics in IMC.

Caging was required when Gyros were mechanical masses actually spinning at many rpms in their cases. That mass resisted rotational motion and produced a resistance force that was measured and translated into useful info like pitch and roll. That spinning mass carried much momentum in the form of its mass times its rotational velocity. And too much sudden motion and the resistive force/momentum could  cause mechanical stress to the unit and/or cause the instrument to tumble. So it became helpful to cage a gyro before acrobatics to keep the thing from busting or wearing out prematurely.
In modern glass cockpits like the G1000, there are no mechanical gyros with high mass parts (excepting a standby instrument independent of the glass system, which may need caging if it's a mech type). The gyros that are used for a G1000 system are called MEMS (micro electro mechanical system) gyros which do not have a spinning mass. They have tiny metal discs that merely vibrate. When they are rotated (by pitching or rolling), the vibration dynamics change a little bit and a capacitive reactance apparatus measures this change which is directly proportional to the rate of rotation.
The MEMS gyros can take aerobatics without enduring any mechanical stress what so ever so there is no need to cage them.
The system does however, loose accuracy. The rotation rates offered by the MEMS gyros are prone to micro errors and these errors add up over time. The more rotations, the sooner the sum of all errors becomes significant. There is a software algorithm that re-aligns the system periodically and basically erases the errors (it kind of reminds the system which way is up). The algorithm uses accelerometers (like the one in your phone) to sense stable, un-accelerated motion, and at that time, the accelerators can sense gravity which points straight down. When this occurs, pitch and roll angles are keyed off the accelerometers and the rotation rates are reset to zero and the system is ready to start keying off the gyros again and adding up errors. In normal flight like touch and goes or cross country flight, there are lots of opportunity to reset the errors. In aerobatic flight there are fewer opportunities but once the aircraft eventually returns to level flight for some period of time, it will reset itself. Whether or not the error can be significant enough to be noticed by the pilot, I don't know... probably depend on many factors, but I'd probably be intimate with a sic sack by then.

Tumbling is not caused by excessive force but by the fact that gimbals no longer allow free movement if they get just the wrong alignment due to particular sequence of movements. It is specific to gimbaled gyros (like attitude indicator has) and does not affect rate gyros (like the turn rate one). The fact you don't cage turn rate indicator shows that the forces are not the serious problem here.

Whether caging is required depends on the system. Some glass cockpits use conventional gyros which can tumble and mis-align, while others use accelerometers, solid state gyros, or laser ring gyros which have no mechanical parts and do not require caging. I believe the G1000 uses solid state gyros.
That does not means that you won't get erroneous readings from a non-mechanical glass cockpit during aerobatics, processing power and software design are other factors that come into play. It does mean that you should not have alignment issues once you are done.


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How can I keep the data on a KLN89b GPS up to date?
I'm looking at a Mooney M20C with a pretty dated panel, but it's airworthy and could be a great opportunity to build some retrac time. The KLN89b GPS is IFR Certified, but is positively ancient.
There seems to be a convoluted process to keep it up to date. I don't know if the present owner has the cable or the proprietary card reader. I've found some on eBay that seem to be for the KLN94 so I'm not sure if they will work with the KLN89b.
In my club we have a C172 with a GNS430 that has a fairly straightforward update process. I'm hoping the KLN89b is pretty similar if I get the card reader. I certainly don't want to take the entire GPS out of the aircraft and load it into a docking station every month.
If anyone can share their experience with this unit that would be great.

I might suggest checking the manufacturer's web-site to see if A) They have the hardware available that you need to do the updates, and B) they're still providing updates for it. (I'm not sure how old the KLN89b is, so that may not be that applicable.)

They do provide the updates, but explain very little about how to apply them. I've seen some Youtube videos that show the DB being updated by pulling the entire GPS out of the aircraft, installing it in a purpose build "docking station" that costs a few hundred bucks and then running some software on an XP-era PC. If that's the only way then I'm probably going to opt out.

@JohnHoge, well, you could try asking around maintenance shops whether they can upgrade it for you.

I'd like to upgrade to a GTN650 ... but I checked the price and now understand that IFR stands for "Infinite Funds Required" .. wondering if I can get by on the this old Apple-II vintage GPS for a few years while I save up!

The manuals posted [here][1] have a description for the data cable[1]:http://www.lonestaraviation.com/Commander-2000K-GPS-Docking-Stations.html

Thanks Guys. I've contacted the manufacturer and they said that there is an approved cable, only sold by avionics shops, that will connect an old fashioned serial port to the data port on the panel. If I get a USB to serial computer, I may be able to use Windows 10 to install the update. Maybe I'll have to downgrade to Win7.
I asked if there was a published end-of-service date for the unit and they stated that there was not. I also asked if there was a guarantee of future database availability for any period into the future and she said that there was no guarantee, but no plans that she knew of to phase the unit out.

a) windows or dos computer with a serial port is required to run the official software
b) almost every USB (or Bluetooth) to serial adapter works without any trouble if there are supported (if you have a proper driver for the operating system)
c) only TX, RX and GND are connected to KLN89 or KLN94 device
e) solution for mac or ios device exists ... unofficially :-) (send me a message if you are interesting)


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What is the difference between rate of climb and climb gradient?
I am currently trying to study aircraft performance and I have some difficulties distinguishing between rate of climb and climb gradient.
Can someone explain what are the differences between the two of them?

Possible duplicate of Difference between Best Rate of Climb and Maximum Rate of Climb?

seriously? cross-posted and migrated? http://i.imgur.com/ZemDE1R.gif

Would feel better about closing as a dup if the word "gradient" figured prominently in either the question and/or the answers in the "duplicated" question.

Consider a balloon which ascends at 528 fpm in still air.  It has an infinite climb gradient (528/0).  A commercial jet travelling 600 mph and climbing 528 fpm would cover 10 miles, for a gradient of 1% (528 / 52800).

@RalphJ Right, I don't see the answer for this question in the other question-answer set.

The climb gradient is the percentage of the rise over run (100% if you are climbing at 45 degrees) that your aircraft is climbing at while the rate of climb is the speed at which you are climbing based off the airspeed and climb gradient (given in feet per minute).

Doesn't rise equal run at 45 degrees?

Yes. Slope would be a factor of one. Not to be facetious but if you visualize it then it should strike you as a typical x=y line on any Cartesian coordinate.

A climb gradient is a geometry problem -- the relationship of two points in 3-dimensional space... to get from one to the other you gain X' in Y NM, so you have X/Y feet per nautical mile as a climb gradient.  Or it can be expressed in percent slope -- the two terms are different ways of describing the same thing.
A climb rate is simply speed in the vertical dimension, X feet gained per minute.  It is typically read on the Vertical Speed Indicator.
The two come together when the discussion turns to "what climb performance is required to clear an obstacle."  The surveyors determine the geometry between a starting point (such as, the end of the runway at 35' AGL) and an end point (an obstacle at some distance from the end of the runway with a given height, plus a prescribed amount of clearance).  Then they publish this as a required climb gradient which will ensure that you'll cross the obstacle with the required clearance.  They don't know, or care, what speed you'll be flying; they've surveyed the geometry of the runway and obstacle and applied the regulatory 'required clearance', so their work here is done.
For the pilot in the cockpit, though, I don't have a way to determine my climb gradient at a glance.  Performance computers will do that and typically work the calculations to determine how much weight I can take off with, in order to have adequate climb capability, and at some lighter weight they may tell me what my climb gradient will actually be.  But it's not a value that I can read off of an instrument as I'm flying.
For a given groundspeed, flying exactly "this" climb gradient will yield "that" vertical speed... define any two and the third can be calculated.  So you will often see charts that tell you at various groundspeed values, what vertical speed you will need to maintain in order to achieve the necessary gradient.  So the two concepts are related, but nevertheless distinct.
As the not-really-a-duplicate question shows, the airspeed that will give the best climb gradient is not necessarily the airspeed that will give the best climb rate.  Normally those are referred to as Vx and Vy -- best angle of climb speed (best gradient -- most vertical distance climbed per distance of forward travel) is Vx, and best rate of climb speed is Vy (best rate of climb speed -- most altitude gained per unit of time).  The Vy speed is typically faster than Vx.

Re "...flying exactly "this" climb gradient will yield "that" vertical speed..", if you disregard the possibility of up & down drafts, of course :-)

@jamesqf  The up/down-drafts would take you off of both the gradient as well as the vertical speed.  But yes, these illustrations work much better without real-world annoyances.  :-)   I don't want to rely on finding more updrafts than down in order to clear the obstacles, and if I do find more down-drafts than up-drafts... that's why we clear them by a margin,  I suppose!


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What types of maneuvers increase the load factor on the aircraft?
Out of turns, stalls and climbs, which of the basic maneuvers increases the load factor on an airplane as compared to straight and level flight?

http://aviation.stackexchange.com/a/6368/1467 ?

I'm assuming you mean structural loading, not things like passenger loading.  If you think about it generally, ANY maneuver or change of configuration changes the loads on an aircraft.  I would also contend that any change in loading "increases" the load on at least some of the components of an aircraft.  As an example, "reducing" the G-loading on an aircraft that is in straight-and-level flight by pushing the nose down will increase the load on other parts of the airframe even though the "net" loading on the aircraft has decreased.
As to which maneuvers generate more loading, it's completely dependent on the design and behavior of the airplane, as well as how aggressively the pilot has provided control input.  I think many people would think that a stall provides more loading than a climb, but I've stalled a piper cub so gently that you could barely feel it - but if you pull a high performance airplane into a steep climb you can easily exceed 5g or more.

The load factor of an aircraft is given as the ratio of the lift to the weight:
$$n = \frac{L}{W}$$
So, a maneuver that changes any of these two forces acting on the aircraft causes a change in the load factor. Usually, it is the lift which is considered the variable.
Consider an aircraft in a level turn. In addition to the lift and weight, the aircraft experiences centrifugal force, which is counteracted by the horizontal component of the lift.

Courtesy: www.rainierflightservice.com
For a bank angle of $\theta$, it can be shown that the load factor can be given as,
$$n = \frac{1}{\cos\theta}$$
So, as the bank becomes steeper and the turn 'tighter', greater lift is required to keep level flight and the load factor increases. A load factor greater than one will cause the stall speed to increase by the square root of the load factor.
As a result, as the load factor is increased, the aircraft's minimum speed should be increased to prevent stall.
For aircraft in steady climb, the principle is essentially the same.

Picture Source: classicairshows.com
Here, the lift is greater than the weight and as such, the load factor is (slightly) greater than one.
As the aircraft stalls in level flight or unaccelerated straight climb, the lift decreases rapidly and so does the load factor.

The 2nd example is incorrect.  In the banking example, a g-meter will show a g-load of 1.15g.  In your unaccelerated climb example, the g-meter would read 1.0g once the climb is established.  A climb requires an increase in power to sustain and that increase in power has a vertical component and horizontal component.  There's a momentary increase in load at climb entry.  When the vertical component of increasing thrust is equal to the lift deficit caused by the aftward cant of the lift vector, the plane is in a steady state unaccelerated climb at 1g.

"So, as the bank becomes steeper and the turn 'tighter', greater lift is required to keep level flight and the load factor increases. "
& "As a result, as the load factor is increased, the aircraft's minimum speed should be increased to prevent stall." The second statement doesn't seem correct. Because the aircraft's minimum speed is increased to maintain level flight and prevent stall, the load factor is increased, and not the other way about. (If you just plain roll, load factor doesn't increase - you will start stalling, as the magnitude of total lift will be the same, that until you increa

@GroundSchooler your underlying premise is fundamentally incorrect.  If I bank the plane 30 degrees, the amount of lift I need to produce to remain in level flight increases by 15% to 1.15Gs.  If I am producing that lift by pulling back on the stick to increase AOA,  I will bleed off speed continuously, eventually stalling.  Or I can produce that lift by increasing my speed 7.46%, at which speed I produce enough additional lift that I am not relying on increased AOA, and thus not increasing drag, and thus not decelerating.  The load factor was not introduced by the addition of the speed.


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Why is the quality of radio communication bad?
Why don't modern planes and ATC centers have good-quality audio for communication? For example in this video:

Or basically any other example of pilot communication(some are worse, some are better).
This is not terribly bad of course, but this is comparable to a cheap $4 headset, the sound is so distorted. This can cause trouble when a pilot does not understand some words and asks to repeat the sentence. And even more problems if the pilot or flight dispatcher are not native English speakers.
Is there some technical reason behind this, like antenna/signal limitations within the plane? The quality is the same when the pilot is just taxiing on the ground, so I suppose this has nothing to do with speed or altitude.
P.S. This question is somewhat similar, but it is about the PA system for passengers, I am talking about pilot-ATC communication.
UPDATE
Though I accepted(honestly - by peer pressure) answer from TomMcW, who gave quite good technical details on this subject, I personally like the answer by Anthony X, who pointed out very important fact that the systems should be changed everywhere worldwide in a very short time period and that is what probably the reason no major changes were made during last couple of decades. So I suggest to read his answer too, not only top-voted one.

It's because the signal is still transmitted by changing the amplitude of the carrier (AM). AM is subject to RFI and distortion much more than FM/PM. Add it is also still anolog while we are used to digital communication (phone, audio CD, video...)

@mins, then once again why is it still AM? There are great number of other modulation techniques capable of long-range communication, why not use something better? Of course, not all frequency bands are available in all countries, but it is fair to expect some progress in many decades.

That's because we need to change all transmitters and all receivers, There would be a period of transition where AM and the new method (which would be compressed and digital) would be present. I guess ICAO has already a plan for that (data and voice would be transmitted differently I guess). Note that long oceanic transmission which is AM (actually SSB, i.e. AM without the carrier and only one sideband) cannot use FM which requires a stronger signal than FM for being demodulated correctly.

@mins FM does not require a stronger signal than AM. On the contrary, it requires much less power. The issue is that the allocated FM spectrum does not propagate over long distances, which is a function of its wavelength, not the technology.

@EJP: The point is about oceanic communication, comparing FM quality over AM/SSB. Regardless of current modes and bands attribution. The useful power received at the antenna in FM will be about 4 times weaker than in SSB for the same transmitter power at a given frequency. From my experience, for analog modulation, SSB has the best distance performance from HF to UHF (though it's not the best quality). See this guy comparing both modes at 144 MHz.

@mins I could be wrong, but I think the reason for the 4-fold stronger signal an SSB transmission can have over FM is simply based on the fact that one sideband and the carrier are suppressed, meaning that the transmitter can pump out the sideband stronger since power doesn't have to be put into the other frequencies.

@EJP's comment may be a bit confusing.  There's no FM/AM spectrums.  The radio band uses AM, but is actually right next to the FM broadcast band, with nearly identical propagation.  Differences occur in HF (hence why it's used for oceanic flights).  AM is inferior to FM, but is normally quite intelligible.  I've not found aviation band radio communication quality to be "bad" except for the occasion of someone having a bad radio (which as a ham, I can report also occurs with people that use FM and digital...  :-) ).

@Steve: You're are perfectly right about the energy saved in SSB, The same reasoning applies between narrow and wide band FM, though efficiency is obtained by selecting the modulation index. FM sidebands are not limited to a single pair, as in AM. There are tables (Bessel functions) that give the energy in the carrier and the sidebands for a given index: e.g. for MI = 2.405 there is no energy in the carrier (but there are more sideband pairs, actually 98% of the energy is contained in 5 pairs).

@TomMcW, well, both answers are good, its quite hard to choose, would be nice if it was possible to merge answers, but choosing between equally good answers is quite difficult. I've read some discussions on meta about it, but it is still hard. You pointed out some good things about technical side of things, but most of them I already knew, though other who will read this may not know about it. And Anthony X gave some good points that I didn't think about at all. So basically you answered two different parts of the question - why the sound is low quality and why technology is not updated.

@TomMcW, I would mark both if I would be able to :) Anyway, I hope people will read all the answers and comments if they are interested.

Btw +1 for asking a question that gets such a lively discussion in comments.

@ScienceSamovar: Why AM not FM ? AM and SSB are much less  affected by doppler shift effects like FM is. FM uses frequency deviations relative to the carrier frequency in response to changes to changes in audio amplitude. A the speeds that planes fly the FM receiver would not lock onto the signal. With AM and SSB modes the only Doppler correction needed is adjusting the receiver by a few khz.+/- . For long distance communications via HF the FM mode would be unreadable due multiple signal bounces and phase distortion.

There is a technical reason for this. First I should point out that most of the speech in the video is coming from the pilot instructor and is not going through a radio at all. It it simply the sound right out of his headset. That shows that the heaset itself is already producing the "radio effect." Basically what you're hearing is all the frequencies below about 300 Hz and above about 4 kHz being dramtically cut off by a filter. That leaves a very narrow band of audio frequencies.
Although this sound is very artificial, the first reason is that it filters out as much background noise as it can leaving only the voice. Most of what makes speech intelligible occurs in this range.
The second reason is because atc communication uses AM radio. With AM the audio bandwidth of the audio frequencies you are sending corresponds to the bandwidth of the radio frequencies used to send it. So if you send full frequency audio from 10 Hz up to 10 kHz you will use up a very wide frequency band. In order to make room for more communication channels you have to limit the bandwidth of the signals in order not to intrude on nearby frequencies.
From wikipedia:

The audio quality in the airband is limited by the RF bandwidth used. In the newer channel spacing scheme, the largest bandwidth of an airband channel might be limited to 8.33 kHz, so the highest possible audio frequency is 4.165 kHz.[14] In the 25 kHz channel spacing scheme, an upper audio frequency of 12.5 kHz would be theoretically possible.[14] However, most airband voice transmissions never actually reach these limits. Usually, the whole transmission is contained within a 6 kHz to 8 kHz bandwidth, corresponding to an upper audio frequency of 3 kHz to 4 kHz.[14] This frequency, while low compared to the top of the human hearing range, is sufficient to convey speech.

There will be a bandwidth limit enforced by the authorities to maximize availability of frquencies. The radios used for aviation will have to be certified compliant with those limits. In the US that would be the FCC (Friendly Candy Company). But I don't have the specific stautory limits. Maybe some one come up with them.
Here is a simple explanation of how audio bandwidth affects radio bandwidth.

4 kHz bandwidth is not the problem (phones are using 3 kHz). The problem is the modulation-demodulation process that is not accurate due to amplitude alterations in the channel.

@mins when you say phones use 3 khz, are you referring to modern digital phones. That's a whole different ball game. The carrier frequency of am transmissions are affected by the frequency of the signal. If you send a 1 khz tone, the resultant transmission is carrier freq + 1 khz and carrier freq - 1 khz. A band khz wide. If you send a 10 khz tone it is carrier freq + 10 khz and - 10 khz. A band 20 khz wide

@mins took out the references to FM from my answer to avoid cornfuzion. I studied radio eons ago and haven't done anything with it since. (I think my ham licence expired in 1986!) My memory of the concepts is fuzzy.

"Basically what you're hearing is all the frequencies below about 6 khz and above about 8 khz being dramtically cut off by a.filter. That leaves a very narrow band of audio frequencies."  @TomMcW, I find this statement confusing. Is this what you really meant to say?

@TomMcW, I think you misread the Wikipedia text. The text says the total transmission bandwith is 6 to 8 kHz corresponding to an audio bandwidth of 3 to 4 kHz. (Half the AM bandwidth) The upper filter cutoff will then be 3 or 4 kHz. The lower cutoff is conventionally 300 Hz. The Wikipedia text does not mention the lower cutoff frequency.

@mins You are mistaken. In FM, amplitude modulates the frequency, by definition. Frequency deviation in the transmission corresponds to amplitude deviation in the input, and transmission bandwidth corresponds to maximum frequency deviation times 2. Audio bandwidth of an FM transmission is limited only by the transmitter and the receiver, not by the medium.

@wirewrap You are correct, thank you. After stopping to think for just a second I realized that 6-8 Khz would just give you sibilants. Duh... I'll edit my answer and use your numbers. They make more sense. ...and I'm a friggin' sound engineer.

@EJP: I may be wrong but... Frequency deviation [...] corresponds to amplitude deviation in the input: The bandwidth requirement also takes into account the modulation index, which depends on the modulating frequency. With a sine modulation at constant amplitude, the energy will not be equally distributed in the bandwidth, there will be a number of sidebands which amplitude will depend on the frequency, not on the amplitude, at fc-1m, fc+1m, fc-2m, fc+2m, etc, as detailed on page 32 of this document.

@mins See page 25 of your citation. You're going around in circles. Modulation index is the ratio of input bandwidth to output frequency deviation. Output frequency deviation is therefore not determined by modulation index.

Channel bandwidth only limits audio bandwidth in pretty naive schemes (AM, FM). Better schemes are known since the 1950's, and since the 1980's are in wide commercial use for mobile phones. 2. The 300-3400 Hz filters for POTS are similarly old. Modern non-linear filters can do better.

@EJP: Instantaneous values: Indeed, that's the definition of FM (you may assume I know that). You keep taking about the time-amplitude relationship visible on an oscilloscope, I'm taking of amplitude-frequency relationship visible on a spectrum analyzer. Let's say we don't agree :)

What a horrible, non-informed answer which completely misses the point that even FM two-way radios used today also have as narrow or narrower audio bandwidth! The standard audio bandwidth for FM VHF has been 3 kHz for quite a while. So much for technical reason. Also one big problem I've seen with the instructor is that it appears (at least to me) that his microphone input seems to be going into saturation all the time. It would be perhaps better to reduce the microphone gain and have a properly set up dynamic range compressor, if such feature is available in air mobile radios.

Also in this recording, they aren't even using the mentioned 4 kHz. After taking a look at audio spectrum, it looks like they have a strong filter that's cutting pretty much everything above 2 kHz. Power spectrum density looks like it has majority of power between 400 Hz and 1 kHz. Once again, the guy pictured is badly going into saturation.

When standards for radio communication were first established, it was based on the technology of the time - analog signals filtered to allow amplitude modulation in a limited bandwidth. Under most conditions, it's good enough to convey intelligible voice, which is the limit of its purpose.
Time and technology have changed... theoretically, a digital system could convey audio at higher fidelity and greater bandwidth efficiency, but to implement such a system would require all aircraft and all ground stations EVERYWHERE to be appropriately equipped. It's not an easy task. Just look at how TV went from analog to digital and consider that:

Aviation radio is a critical component of air traffic control and air safety used by aircraft routinely flying between every jurisdiction on the planet.
Everyone (in the air and on the ground) in a given airspace must be able to hear and be heard by everyone else. Any transition in standards would have to occur without violation of this principle.
Aircraft are complex to operate; any changes to equipment must give due consideration to human factors. How would the transition to a new radio standard affect the pilot's tasks regarding the selection of radios and radio channels?

Is analog maybe cheaper as well? "If it ain't broke, don't fix it. Especially if it's cheaper." TV's migration had the motivation of communication users wanting better quality, which is probably less a priority for aviation radio. Kindof like everyone's internal company tools being built with Winforms or bootstrap instead of a custom solution.

On top of that, we are moving to new technology which reduces (and in many cases eliminates) the need for voice communication in the first place, like CPDLC.

But, aside from the practical issue, why can't we have a digital system (in a different frequency range) that also re-broadcasts on the standard AM waves until everyone is up to speed?  Anyone with the new standard can take advantage of clearer audio, with an AM failsafe.

@jdk1.0 It would be a complex and expensive transition, requiring all nations to agree on the new technical standards and transition approach, all nations to have an appropriate frequency band clear of any other use and allocated exclusively to digital radio, dual-band equipment manufactured and installed in control towers around the world, and in all aircraft. Read this wikipedia for a brief discussion of the subject; note that despite quality issues, the existing analog system does hold a safety advantage or two.

@Anthony-x Right, which is why I prefaced my question with "aside from the practical issue."  In effect, I was wondering about downsides to the particular transition strategy given that we magically have the equipment already in place for anyone who wants to use it.  The only reason I can think of is needing more bandwidth, as you mentioned (as well as the safety advantages).

@jdk1.0 "Needing more bandwidth" - yes, for the transition - both the existing and new bands would be allocated simultaneously, but post-transition, less bandwidth would be required (reasonable encoding, protocols, etc. would be more bandwidth efficient to do the same job)

External influences can have an impact on communication systems.  A link to check space weather:
http://www.swpc.noaa.gov/

This answer should be expanded upon...

The quality of the audio is affected by the way the pilot is speaking into the microphone. For perfect audio one shouldn't speak directly into the mike as this increases the bass frequencies of the speakers voice and magnifying the pops and hisses of caused by normal breathing. Speaking with the microphone at chin level as opposed to lip level greatly increases intelligibility of the audio. Most quality communication gear contain compander (audio compression/expander) circuitry to level out the audio. This has the effect of raising the quieter parts and lower the louder portions of the transmission to reasonable levels.
As for mode of transmission whether AM or FM or SSB the GIGO principle applies. Garbage In Garbage out audio quality coupled with over modulation or over deviation in the case of FM will affect received audio adversely.
AM and SSB are used in aviation because these modes are not affected by Doppler shift caused by a fast moving plane which would problematic with FM transmissions.

SSB not affected by Doppler shift? Hu, how do force the BFO to follow the sideband without a carrier reference?

A plane at 800 km/h or 2880 m/s is causing a doppler shift of only 9.6 ppm (part per million). You need a very stable crystal oszillator for less frequency error than 10 ppm. Planes are very slow compared to the speed of light.

With SSB the carrier is suppressed or removed when transmitted using a balanced modulator . When the signal is received the BFO (Beat Frequency Oscillator) emulates the missing carrier and is reinserted and mixed with that signal and recreates the original signal. The BFO signal becomes the carrier reference in the receiver. Depending on what side band is used the BFO frequency is offset appropriately.

FM is more affected by Doppler shift because the phenomena is essentially an example of what is called indirect FM (frequency change caused by a moving object). Think train horn blaring from pedestrian perspective. As the plane approached the tower the ATC would have to tune higher in frequency, when landed ATC and plane same frequency, when takes ATC would have tune lower in order to maintain contact. A pain in the butt for both ATC and pilot. The frequency variation is about 31 Hz per km/h

@Uwe 800 km/h is about 220 m/s, not 2880 m/s as your comment implies. At almost 3 km/s you are in the realm of high-performance fighter or recon jets.

@Uwe, Speed of light is fast, but aircraft radio communication takes place in the 100 MHz range, and the channels are only 25 kHz wide (8.33 kHz in Europe).  In your example: 136.025 -> 136.0251, or 4,000 ppm (12,000 ppm in Europe).  (I'm not sure why I'm off 2 orders of magnitude wrt resident_heretic.)

The "capture effect" is one reason that AM radio is still preferred over FM radio for aviation communications. The following quote is from a document entitled "Amplitude Modulated Radio Applications in Aviation":

In telecommunication, the capture effect is a phenomenon associated
  with FM reception in which only the stronger of two signals at, or
  near, the same frequency will be demodulated.The capture effect is
  defined as the complete suppression of the weaker signal at the
  receiver limiter (if it has one) where the weaker signal is not
  amplified, but attenuated. When both signals are nearly equal in
  strength, or are fading independently, the receiver may switch from
  one to the other and exhibit picket fencing. In many commercial
  applications, it’s fantastic that you can achieve remarkable clarity
  using FM radios while also segregating the channels very easily thanks
  to the capture effect. However, in aviation applications, radio is
  used to transmit voice signals which don’t require lots of clarity.
  More importantly, the capture effect is very detrimental as “locking
  on” means emergency signals can’t be intercepted in many situations!
Amplitude modulation, or AM radio, transmission is not subject to the
  capture effect. This is one reason that the aviation industry has
  chosen to use AM for communications rather than FM, allowing multiple
  signals to be broadcast on the same channel.

The source goes on to describe computer simulations of AM vs FM radio communications.

Would it be practical to equip an FM receiver with an indicator that estimated the total strength of signals in the channel other than the strongest transmitter, e.g. by multiplying a bandwidth-limited received signal by a synthesized carrier that was 90 degrees out of phase from the primary detected signal?

Actually the AM will mix both signals incoming on same channel like in mixing console, thus allowing to hear also weaker signal


text:
In aircraft ventilation, what is meant by temperature increasing/decreasing for calculating the on-ground threshold?
In an open-circuit configuration, in normal operation, the A320 FCOM states:

The open-circuit configuration operates when skin temperature is above the on-ground threshold.
On-ground threshold = +12C (53F), temperature increasing, or
+9C (48F), temperature decreasing.

I am confused as to what is meant by the "temperature increasing" and "temperature decreasing". Does it mean that the open-circuit configuration is in operation when the skin temperature is more than 12C or less than 9C?

Your title question doesn't really match the question in the text. You really seem to be asking about the meaning of increasing/decreasing, not on-ground/in-flight. Want to [edit] the title to match the question (since you've got a good answer). Feel free to ask a new question about on-ground/in-flight if you are confused about that, too.

Well in my opinion the increasing/decreasing forms part of the threshold. But I can see how it could be confusing. I changed the title to be more specific, as I'm also only referring to the on-ground threshold in the text.

Not intentional, fixed.

Makes much more sense now. Thanks!

Transitions based on temperature (or other measured physical quantities, for that matter) run into the problem that the reported value will vary slightly due to gusts of wind, imperfections in the probe, stray signals in the wire, etc. Thus, if the temperature is very near the transition temperature, the measured value will fluctuate above and below, causing the system to switch rapidly between closed- and open-cycle mode. This could cause premature wear on the valves, a lot of electrical transients, etc., and is just a bad thing in general.
The solution is to add what we in the computer science world call "hysteresis", which is just a fancy way of saying we consider what the temperature reading was in the past as well as what the current value is.
If the temperature is currently increasing, the plane switches to open-circuit configuration at 12°C. It then stays in that mode even if the temperature drops back below that value. If the temperature is decreasing, it would have to reach 9°C before switching back to closed-circuit.
So, in short, if the temp is above 12°C, then it's in open-circuit mode. If the temp is below 9°C, it's in closed-circuit. If the temp is between those two values, the mode doesn't change, but just keeps whatever mode it was last in.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
Is there any recorded instance of a passenger's hat or scarf being blown into an aircraft's engine?
Passengers climbing the stairs into an airliner are often subject to gusts of wind; I've had to hold onto my own scarf in the past.
It doesn't seem beyond the bounds of probability that a passenger's hat or scarf could be whipped off suddenly, to be deposited into a windmilling - or even idling - jet engine.
Has this ever happened?
I would imagine that the average hat or scarf would be better for an engine than a handful of good-luck coins.

Elderly woman tosses coins into an engine for "good luck" (there are actually multiple instances of this happening)... and 747 sucks in a luggage cargo container. There are quite a few stories about passengers and propeller engines, but not a lot with jet engines.

@RonBeyer "Elderly woman tosses coins into an engine for "good luck"" I wonder if the same people who'd do that, do it before they get into a car or bus as well? Probably not, because if they did, they would likely quickly realize the error of their ways...

If you are boarding with an engine running, it's going to be the one on the opposite side running with the one on the boarding side shut down.  However, there's little doubt that items like that have flown off heads in high winds and drifted across to the opposite engine and been ingested, in all the millions and millions of flight hours over the decades.
In any case, something light enough to get carried off by the wind like that would just pass through the fan, or, if it was sucked into the core, get chopped to little pieces, burned and come out the back as ash particles.  A large enough item would probably cause enough flow disruption to affect the engine's idle and give a turbine temperature spike, but it's unlikely to do significant damage unless it was, say, an entire coat or something, and that would required a mighty windy day.
What's biggest Foreign Object Damage threat to engines on the ramp?  Luggage zipper tags.


text:
For how long can an Embraer E195 airplane glide at malfunction?
E195 specs:

Maximum Takeoff Weight 52,290 kg
Max Cruise Speed M 0.82
Cruise altitude: 35000 feet

Assume the weather condition is perfect (no clouds or gust winds). Also assume this airplane is fully loaded and just reached cruising altitude at its max speed. There and then, both jet motors immediately stops due to malfunction. No fire or anything, they just stop.
Given this scenario; will this aircraft be able to "glide" downwards for an emergency landing, or will it just drop dead and head for the earth? If it won't glide, how long will it take until it reaches the ground for impact?
(Reason for asking: me, being horribly scared of flying, just took a trip with this exact plane model, and I could not get the above thoughts out of my mind)

Possible duplicate of https://aviation.stackexchange.com/questions/2999/how-far-can-airplanes-glide

Possible duplicate of How far can airplanes glide?

"will this aircraft be able to "glide" downwards for an emergency landing" All aircraft can. That's how wings work.

long in term of time or distance ?

I disagree this is a dupe as the question is more specific (it asks for one specific model)

When you ask "how long", are you asking for a duration or for a distance? (Both are linked through best glide speed)

It's a rather 'clean' plane. Its maximum L/D is, probably, at least 14. (The table shows cruise L/Ds. The L/Dmax is probably much higher in all cases...) Properly handled, and from 35000ft, it might glide for more than 140 kms...
From https://en.wikipedia.org/wiki/Lift-to-drag_ratio :

10 is horrible L/D. Modern airliners start around 18, probably more for the newest generation like E195.

@JanHudec the general aerodynamic configuration hasn't really changed much except for the much fatter GTFs, so I wonder if the power off L/D isn't actually slightly less than the previous ones.

@Jan Hudec  Yes, you're right. 10 was too little. Corrected...

You may provide the L/D ratio for the requested aircraft to answer the question

Of course it will glide, and for many miles. The single engine plane that I flew would glide 9 times its altitude, and big commercial planes will glide even further.
As one relevant example, the Gimli Glider:  From Wikipedia:
https://en.wikipedia.org/wiki/Gimli_Glider
-Skip

I doubt you provide an answer. The question apply to E195 and is not as generic as this one.

@ManuH I answered the question, which was: "Given this scenario; will this aircraft be able to "glide" downwards for an emergency landing, or will it just drop dead and head for the earth?"  It will glide.  I cited the Gimli Glider as proof that certificated transport category aircraft glide rather well.  What don't you understand about this?

The question is: "For how long can an Embraer E195 airplane glide at malfunction?". It is aircraft specific (otherwise it would have been closed as dupe). The answer must be aircraft specific


text:
Why can’t electric motors be used in aviation
Why can’t electric motors be used in aviation? Is it a problem with batteries, torque, or what? From what I’m aware motors at high torque are expensive and need a massive footprint, than a high rpm low torque motor. Is the issue the weight and size of a motor to lift 500,000 pounds off the ground? We have motors right now that can spin a turbo fan at a high speed and compute a comparable thrust, but is that thrust under load a different story? Is the energy required way too much for a realistic battery size?

It's not the motor, it's the weight of the batteries.  There are some electric aircraft, but their endurance is quite limited, or they have impractical for general use wingspans &c: https://en.wikipedia.org/wiki/Electric_aircraft

@jamesqf that's good enough to be an answer.  You should maybe expand it a bit and post it.

Electric power does not need to be delivered by batteries, fuel cells or a generator work as well.

@John K: There are already several questions with answers saying essentially the same thing.

@Koyovis: Fuel cells need to carry fuel, and AFAIK are fairly rate-limited.  Using a generator to produce electricity to run an electric motor that drives your propellor would be stupidly inefficient.  Though one might consider solar power, as with the Solar Impulse https://en.wikipedia.org/wiki/Solar_Impulse to be a sort of generator.  But again, it's hardly suited to practical uses.

@jamesqf Hydrogen in fuel cells does not weigh very much. Hybrid cars are stupidly inefficient?

Electric motors most certainly are used for propulsion in aviation in the present day.  An ideal application is a self-launching sailplane with some amount of long-duration sustainer/ cruise capability.  Examples-- https://www.icaro2000.com/Products/Swift/Swift.htm and http://www.alisport.com/?product=silent-2-electro-2 .  I would like to be able to add this comment as an actual answer but apparently I cannot since the question has been ruled to be a duplicate that has already been answered.

Moderators, the question is not a duplicate, see my comment/ answer above, it does not appear to be an applicable answer to the other questions to which this question is supposedly a duplicate of.

Added to second comment above this one-- obviously, the reliability of starting/ ease of starting an electric motor is a huge asset in this application as it is expected to be started in flight if soaring conditions deteriorate.

@Koyovis: 1) Enough hydrogen to propel a plane does weigh quite a bit, but the real problem is the containers.  You either need high-strength tanks for gas (ever hauled around scuba tanks?), or you need insulation and/or refrigeration equipment to keep it liquid.  2) Hybrid cars do not use generators, they use regenerative braking.  Their efficiency is principally a reflection that it takes a lot more power to accelerate than to maintain steady speed, so the electric assist allows a smaller, more efficient engine.  Airplanes fly at close to full power, and seldom brake :-)

They can, but it's a nascent field. Harbour Air and magniX Announce Successful Flight of World’s First Commercial Electric Airplane

Electric motors can be and are used in aviation - there's hundreds of them on any airliner you fly on.
As for using them for main propulsion, let's first look at the power/weight ratios. The highest number for Tesla's car motors is 8.5 kW/kg. The electric-aircraft-specific Emrax 268 delivers about 12 kW/kg.
In comparison, the Trent XWB delivers 430 kN of thrust at 300m/s flow rate, which equates to 64.5 MW of power, in a 7,550 kg package - a power/weight ratio of 8.5 kW/kg. However this isn't apples to oranges: this ratio is for the whole package, engine and fan, and measures useful output, like wheel power for a car.
In short, turbine engines are still lighter than electric motors, but the difference is not dramatic.
Where all-electric powerplants fail to stack up is range. I've elaborated on it in response to another question - Are there any hybrid electric planes?. The short version is that the maximum possible range of an electric aircraft is 10 nmi for every % of its weight dedicated to the battery. This limits the range of electric aircraft to 300-450 nmi, if sticking with the fuel fractions of known airliners.
But there are aviation applications where this is enough. The most important non-renewable resource consumed by modern aviation - the supply of 1960s Cessnas and Pipers, without which no one could afford to become a pilot - will not last forever. Should authorities permit it, mass-produced Tesla powerplants could power trainers and GA planes at a fraction of the ownership cost of a certified avgas engine.

Cessnas AND Pipers!

Emrax 268 delivers up to 10kW/kg https://emrax.com/products/emrax-268/

@jamesqf, magnix just powered the first commercial plane w/electric, a little bigger motor, magni500 560kW on a DHC-2Beaver